This invention relates to ring seals used in gas turbine engines and methods for making such ring seals.
A typical prior art ring seal used to seal between a seal plate and a turbine rotor in a gas turbine engine is shown in FIG. 1. Referring to this figure, a turbine rotor 10 consists of a wheel portion 12 which is coupled to other rotating components in the engine by curvic couplings 14. In a manner familiar to those skilled in the art, at its radially outer periphery 16, the rotor 10 has a plurality of circumferentially disposed fir-tree grooves. Each of these grooves receives a correspondingly shaped root of a blade 20. The outer surface of the periphery 16 disposed between adjacent blades is referred to as a disk post 18, which is shown in FIG. 2. A rotating seal plate 22 abuts the periphery 16 of the rotor 10. Two conventional ring seals 24 are used to prevent leakage between the seal plate and the rotor. These seals are typically a simple split ring of nickel and are commonly used in gas turbine engines.
The blades 20 are usually mounted in the grooves at an angle that is offset from the axial axis of the engine. This angle is referred to as a broach angle. For highly loaded turbine rotors (i.e. those subject to high stresses due to high rotational speeds), the broach angle causes a net moment on the individual disk posts which may cause the posts to twist significantly. This twisting results in a sawtooth pattern between blades and disk posts as viewed from above and circumferentially around the rotor. For illustrative purposes, this sawtooth pattern is exaggerated in FIG. 2. The actual offset between the disk post and adjacent blades typically does not exceed 0.004 inches. Referring to this figure, because of the sawtooth pattern, triangular leakage areas 26 form between seal rings and the rotor periphery. Conventional nickel rings seals are not pliable enough to deform and fill these leakage areas resulting in a performance penalty to the engine.
Accordingly, there exists a need for a seal ring that is deformable so as to be able to fill these triangular leakage areas.
An object of the present invention is to provide a deformable seal ring.
Another object of the present invention is to provide a method for making a deformable seal ring.
The present invention achieves this object by providing a ring seal having a nickel or cobalt core covered by a layer of a noble metal, preferably platinum. This layer further includes a dense inner layer and a porous outer layer both of which plastically deform in the presence of a load.
A method for making such a seal is also disclosed. The method starts with a nickel or cobalt wire ring and includes the following steps.
coating said ring with a first layer of platinum to form a dense platinum layer;
optionally heating said coated ring until said platinum and nickel diffuse together;
applying a second layer of porous platinum over said first layer by electroless plating said coated ring in a platinum bath comprising 0.8-1.2 gram/liter platinum as diammine dinitrite salt Pt(NH3)2(NO2)2, 50-100 milliliter/liter of 25% ammonium hydroxide NH4OH; and 0.3-1.5 gram/liter hydrazine hydrate N2H4H2O, at a temperature in the range of 75-90xc2x0 C. and at a plating rate in the range of 0.5-3.0 micron/hour with the total thickness of the platinum layer being in the range of 0.002 to 0.006 inch.
heating said twice coated ring in an inert atmosphere until the included hydrogen in the porous platinum layer escapes creating a metallurgical bond between the core and the inner dense platinum layer and until the platinum is annealed, (i.e. softened);
cooling said twice coated ring and mounting said ring between said structures; and
plastically deforming the ring when place under load in an engine or other application.
These and other objects, features and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings.